全文获取类型
收费全文 | 4939篇 |
免费 | 244篇 |
国内免费 | 51篇 |
专业分类
化学 | 3449篇 |
晶体学 | 34篇 |
力学 | 126篇 |
数学 | 922篇 |
物理学 | 703篇 |
出版年
2023年 | 47篇 |
2022年 | 101篇 |
2021年 | 136篇 |
2020年 | 121篇 |
2019年 | 94篇 |
2018年 | 89篇 |
2017年 | 81篇 |
2016年 | 183篇 |
2015年 | 172篇 |
2014年 | 208篇 |
2013年 | 360篇 |
2012年 | 337篇 |
2011年 | 427篇 |
2010年 | 282篇 |
2009年 | 231篇 |
2008年 | 329篇 |
2007年 | 327篇 |
2006年 | 265篇 |
2005年 | 236篇 |
2004年 | 212篇 |
2003年 | 160篇 |
2002年 | 160篇 |
2001年 | 75篇 |
2000年 | 45篇 |
1999年 | 55篇 |
1998年 | 32篇 |
1997年 | 49篇 |
1996年 | 49篇 |
1995年 | 34篇 |
1994年 | 29篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 11篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 11篇 |
1972年 | 9篇 |
排序方式: 共有5234条查询结果,搜索用时 0 毫秒
21.
Manuel Fernández-López Eduardo García-Río Demir N. Kupeli 《Annals of Global Analysis and Geometry》2002,21(1):1-13
A characterization of time functions on a spacetime is made by using theMöbius equation. It is shown that a time function characterized in this wayyields past timelike geodesic incompleteness and local Lorentzian warpedproduct decomposition of spacetime, provided that the stress-energy tensoris a fluid. Also, by imposing additional assumptions on the stress-energytensor and global analytic structure of the spacetime, more restrictivedecompositions closer to Robertson–Walker spacetimes are obtained. 相似文献
22.
Manuel Barros 《Annals of Global Analysis and Geometry》1992,10(3):219-226
In this paper we deal with the following particular case of a weaker conjecture by B. Y. Chen: Are there 2-type Willmore surfaces in E 3? In particular we prove that the above question has a negative answer when the surface is the image under stereographic projection of a minimal surface in S 3. 相似文献
23.
Isabel Brandariz José L. Barriada Teresa Vilari?o Manuel E. Sastre de Vicente 《Monatshefte für Chemie / Chemical Monthly》2004,343(6):1475-1488
Several reported procedures for calibrating glass electrodes in proton concentration are compared. Some recommendations for non-experts are also given. The examined procedures can be classified into two broad categories, namely: those based on direct potential difference measurements of solutions of known proton concentration and those that use one or several pH standards to calibrate the electrode and subsequently measure the pH of solutions containing known proton concentrations. With a single buffer, the two types of procedures lead to equivalent results. However, if two pH buffers are used, the slope of the calibration graph in proton concentration will differ from the real electrode slope to an extent proportional to the difference between the liquid junction potentials of the two buffers. Therefore, any other method is preferable under these circumstances. 相似文献
24.
25.
Manuel Santos-Trigo 《ZDM》2007,39(5-6):523-536
Research programs in mathematical problem solving have evolved with the development and availability of computational tools. I review and discuss research programs that have influenced and shaped the development of mathematical education in Mexico and elsewhere. An overarching principle that distinguishes the problem solving approach to develop and learn mathematics is to conceptualize the discipline as a set of dilemmas or problems that need to be explored and solved in terms of mathematical resources and strategies. In this context, relevant questions that help structure and organize this paper include: What does it mean to learn mathematics in terms of problem solving? To what extent do research programs in problem solving orient curricular proposals? What types of instructional scenarios promote the students’ development of mathematical thinking based on problem solving? What type of reasoning do students develop as a result of using distinct computational tools in mathematical problem solving? 相似文献
26.
Large-scale production of cellulose-binding domains. Adsorption studies using CBD-FITC conjugates 总被引:1,自引:0,他引:1
Ricardo Pinto Joana Carvalho Manuel Mota Miguel Gama 《Cellulose (London, England)》2006,13(5):557-569
A method for the gram-scale production of cellulose-binding domains (CBD) through the proteolytic digestion of a commercial enzymatic preparation (Celluclast) was developed. The CBD obtained, isolated from Trichoderma reesei cellobiohydrolase I, is highly pure and heavily glycosylated. The purified peptide has a molecular weight of 8.43 kDa, comprising the binding module, a part of the linker, and about 30% glycosidic moiety. Its properties may thus be different from recombinant ones expressed in bacteria. CBD-fluorescein isothiocyanate conjugates were used to study the CBD-cellulose interaction. The presence of fluorescent peptides adsorbed on crystalline and amorphous cellulose fibers suggests that amorphous regions have a higher concentration of binding sites. The adsorption is reversible, but desorption is a very slow process. 相似文献
27.
28.
Amorín M Castedo L Granja JR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6543-6551
Here we report the preparation and structural characteristics of self-assembling peptide tubelets composed of 32-membered rings formed of alternating alpha-amino acids and cis-3-aminocyclohexanecarboxylic acids. The tubelets possess a partial hydrophobic core environment, provided by the projection of the cyclohexane C2 methylene moiety into the lumen, and a Van der Waals pore diameter of about 7 A. 相似文献
29.
The synthesis of 2,8-dimethyl 3,9-dichloro 6-sila[5.5] spiro undecatetra 2.4,8,10-ene is described. The thermal decomposition of the adduct formed by the reaction of this product with methyl acetylene dicarboxylate is studied. From the characterization of the copyrolysis products, two possible mechanisms are proposed which imply the formation of digonal silicon such as 2-silaallene and 2-silaketene. 相似文献
30.
The chemical behaviour of sila-2 butadienes, formed as transient intermediates either by thermolysis or by photolysis of various 1-vinylsilacyclobutanes, was studied with respect to hydroxylated compounds of different pKa values Two mechanisms can explain the nature of the products obtained on the co-thermolysis of the cyclic compounds with phenol, one with 1-silacyclobut-1-ene intermediate and the other involving an allylic silicenium cation. In both hypothetical mechanisms, the 2-silabutadienes behave as a conjugated system since they lead either to (2+2) cycloaddition or to (1,2)- and (1,4)-electrophilic addition. This evidence for a conjugation phenomenon through a silicon atom is supported by the calculation of the delocalisation energies of butadiene and 2-silabutadiene. 相似文献